This section is intended to provide a background or context to the invention disclosed below. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise explicitly indicated herein, what is described in this section is not prior art to the description in this application and is not admitted to be prior art by inclusion in this section. Abbreviations that may be found in the specification and/or the drawing figures are defined below at the end of the specification but prior to the claims.
Machine-to-machine communication (M2M) or LTE machine-type communications (MTC) allow “machines” such as wireless devices, typically referred to as UEs, to communicate with each other. Meanwhile, millimeter wave (mmW) communication systems could be one of the potential 5th generation (5G) networks. These are important wireless communication technologies.
For MTC, there is a special interest group (SIG) formed with industry partners, operators and vendors that is set to agree on next-generation MTC standards, which will be proposed to 3GPP Rel. 13. The targets for the M2M SIG include the following:                Enhanced coverage for MTC with special focus on meter reading devices with up to 20 dB additional coverage relative to current meter reading devices;        Low cost devices, the complexity of which should be low enough to enable building of MTC UE devices for less than one dollar in United States currency; and        UE current consumption should enable battery lifetime up to 20 years based on two AA batteries.        
MTC devices in enhanced coverage mode usually need to transmit full power to meet the challenging uplink link budget. However, certain PA power back off power is needed to avoid transmission distortion, which will reduce the maximum transmission power of the UE. That is, many power amplifiers (PAs) are devices that tend to have higher distortion (e.g., nonlinearities) the higher the power output, at least over some range near the maximum output power of the PA. Assuming that distortion is a problem for a signal, intuitively, if a first signal has peaks that are close to an average value of the first signal, the average value of the first signal may be closer to the maximum power output of the PA while having a certain amount of distortion, as many of the peaks of the signal should not or will not enter the power output area of the PA where distortion occurs. However, if a second signal has peaks that are farther away from the average value of the second signal, the average value of the second signal will have to be farther away from (relative to a position of the first signal) the maximum power output of the PA while having the certain amount of distortion, as many of the peaks of the signal might otherwise enter the power output area of the PA where distortion occurs. The first signal (with less signal “spread” between the peaks and average) would typically have less power back off than would the second signal (with more signal spread between the peaks and average), which would have a relatively higher power back off.
There are a number of measures that quantify the waveform of a signal to determine what the spread of a signal is. The PAPR (peak-to-average power ratio) is one such measure, and is typically defined as the peak amplitude squared (providing the peak power) divided by the RMS (root-mean-square) value squared (providing the average power). The PAPR of a transmitting waveform will therefore determine PA back off power and thus the PAPR will affect the MTC UL coverage performance.
For a mmW network, due to high path loss over millimeter wave transmission, a cell-edge UE is usually transmitting full power with power back off. Similar to MTC devices, the PAPR property of the UE Tx waveform is also essential for mmW UL transmission.
Therefore, it would be beneficial to improve the PAPR property of modulation waveforms.